Motor drive control device and operating method thereof

ABSTRACT

The present invention properly starts up various types of motors under operating conditions where motor operations are performed in a wide range of temperature and power supply voltage. Output drive controllers supply PWM drive output signals to the output pre-driver in such a manner as to minimize the error between a current instruction signal and a current detection digital signal. In response to a detected induced voltage generated from a voltage detector upon startup of a motor, an initial acceleration controller supplies initial acceleration output signals specifying a conducting phase for initial acceleration of the motor to the output drive controllers. The initial acceleration controller, the output drive controllers, and an output driver make a conducting phase change and perform a PWM drive to provide the initial acceleration of the motor in response to the detected induced voltage and to an error upon startup of the motor. Upper-limit duty values for the PWM drive output signals to be supplied from the output drive controllers to the output pre-driver during the period of the initial acceleration can be arbitrarily set in the output drive controllers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2012-017930 filed onJan. 31, 2012 including the specification, drawings, and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a motor drive control device thatdrives a three-phase DC motor. The present invention also relates to amethod of operating the motor drive control device. More particularly,the present invention relates to a technology effective for properlystarting up various types of motors under operating conditions wheremotor operations are performed in a wide range of temperature and powersupply voltage.

A brushless three-phase DC motor is used as a spindle motor for rotatinga magnetic disk of a hard disk drive (HDD). The spindle motor rotatesthe magnetic disk at a high speed, positions a read/write magnetic headclose to the surface of the rotating magnetic disk, and moves themagnetic head in the radial direction of the magnetic disk to writeinformation on the magnetic disk and read the information written on themagnetic disk.

When a brushless three-phase DC motor was subjected to drive control inthe past, a Hall element was used to detect the positional relationshipbetween a rotor (rotating part) and a stator (stationary part). Reversemotor rotation was prevented by determining an appropriate conductionstart phase by selecting it from three coil phases in accordance withthe detected positional relationship. However, when a rotor positiondetector based on the Hall element was incorporated in the motor, it wasdifficult to reduce the size of the motor. Hence, a sensorless DC motorwas frequently used for the hard disk drive. If the positionalrelationship between the rotor and the stator is not properly determinedat the beginning of rotation, such a sensorless DC motor may cause therotor to rotate in a reverse direction.

A conduction start phase determination method described in JapaneseUnexamined Patent Publication No. 2001-275387 sequentially supplies ashort pulse current in a forward direction and in a reverse direction tothe extent that a rotor does not respond to the field coil of each phaseof a brushless motor, combines a voltage induced during aforward-direction supply with a voltage induced during areverse-direction supply, which are both developed in a non-conductingphase, determines the polarity of the combined induced voltage, anddetermines a conduction start phase in accordance with the determinedpolarity. The induced voltage is a voltage that is induced on a fieldcoil of a stator by the magnetic field lines of a magnet for the rotorin accordance with the positional relationship between the rotor'smagnet and the stator's field coil. Currents flowing to the field coilsof two out of three phases are sequentially alternated between forwarddirection and reverse direction to compare the resulting inducedvoltages. This makes it possible to determine which of the field coilsof the two phases is closer to a pole of the rotor's magnet anddetermine whether the pole is an S-pole or an N-pole. Meanwhile, thereverse voltage (back electromotive voltage) of the motor is a voltagethat is developed across a field coil of the stator in proportion to arevolving speed when the rotor's magnet rotates in a magnetic field ofthe stator's field coil. The reverse voltage of the motor is essentiallydifferent from the induced voltage of the motor.

FIG. 13 in Japanese Unexamined Patent Publication No. 2006-115599 andthe description given with reference to this figure deal with motorstartup control that includes a sequence of initial rotor positionidentification and conducting phase determination by a three-phasesense, motor drive by conduction, rotor movement verification by athree-phase sense, motor drive by conduction, rotor movementverification by a three-phase sense, and motor drive by conduction. Thethree-phase sense is accomplished by supplying a short pulse current inthe forward direction and in the reverse direction to the extent thatthe rotor does not respond, subjecting an induced voltage developed inthe remaining non-conducting phase to analog-to-digital conversion, andadding up the results of analog-to-digital conversion with anintegrating register.

In the first three-phase sense for identifying an initial rotorposition, the polarity of an induced voltage in each non-conductingphase of a total of three phases is determined to determine theconduction start phase in accordance with the determined polarities ofthe induced voltages in the three phases. When the motor is driven byinitial conduction, the field coils of two phases that are determined asa conduction start phase by the first three-phase sense is energized fora relatively short predetermined period of time to subject the motor toa first initial acceleration. The second and third three-phase senseoperations are performed to check for the reversal of polarity of aninduced voltage concerning the next detection phase, which is determinedfrom the conduction start phase.

FIG. 3 in Japanese Unexamined Patent Publication No. 2008-113506 and thedescription given with reference to this figure deal with a motorstartup method that reduces the time required for motor startup bypreventing the generation of noise during motor startup, which isdetermined by the sum of a three-phase sense detection period forinitial acceleration described in Japanese Unexamined Patent PublicationNo. 2006-115599 and a conduction period for motor drive. In other words,the polarity of an induced voltage in each non-conducting phase of atotal of three phases is determined by one three-phase sense operation,as is the case with the description given in Japanese Unexamined PatentPublication No. 2006-115599, and the conduction start phase isdetermined in accordance with the determined polarity of the inducedvoltage in each of the three phases. In subsequent PWM drive forconduction for motor drive, the induced voltage developed in anon-conducting phase is detected so that the conducting phase is changedin response to the detection of the peak of the induced voltage. Evenafter the conducting phase is changed, the peak of the induced voltagedeveloped in a non-conducting phase during motor drive is continuouslydetected. The detected peak is then used to time a phase change for thepurpose of accelerating the motor.

SUMMARY

Before the disclosure of the present invention, the inventors of thepresent invention have been engaged in the development of asemiconductor integrated circuit called a motor driver IC that rotates amagnetic disk of a hard disk drive (HDD) capable of starting up varioustypes of motors under a wide range of operating conditions.

The development has been conducted in a situation where it is demandedthat various types of motors properly start up without regard to a widerange of changes in the temperature and in the power supply voltage.However, the inventors engaged in the development have found that whenthe motor startup method described in Japanese Unexamined PatentPublication No. 2008-113506 is used, it is difficult to properly startup various types of motors under operating conditions where motoroperations are performed in a wide range of temperature and power supplyvoltage.

FIG. 13 is a diagram illustrating the configuration of a motor drivecontrol device for driving a three-phase DC motor, which has beenstudied by the inventors of the present invention before its disclosure.

As shown in FIG. 13, voltage sources, which equivalently exhibit reversevoltages B-emf (U), B-emf (V), B-emf (W), are coupled to one ends ofstator coils of a motor (MT) 1, namely, a U-phase stator coil LU, aV-phase stator coil LV, and a W-phase stator coil LW. The other ends ofthe U-phase stator coil LU, V-phase stator coil LV, and W-phase statorcoil LW of the motor (MT) 1 are commonly coupled as a midpoint.

The motor drive control device shown in FIG. 13 includes a virtualmidpoint generator 2, an induced voltage detector 3, an A/D conversionsection 4, an initial acceleration controller 5, an output drivecontroller 6A, a PWM modulator 6B, a drive voltage generator 6C, aparameter setup register 7A, a serial port 7B, an output driver 8, acurrent detector 9A, and a sense amplifier 9B.

The stator coils LU, LV, LW of the three-phase motor (MT) 1 are PWM(Pulse Width Modulation)-driven by the output driver 8. Morespecifically, the output driver 8 includes a spindle output pre-driver81, pull-up power MOSFETs M1, M2, M3, and pull-down power MOSFETs M4,M5, M6. The U-phase stator coil LU of the motor (MT) 1 is driven by thepull-up power MOSFET M1 and the pull-down power MOSFET M4. The V-phasestator coil LV of the motor (MT) 1 is driven by the pull-up power MOSFETM2 and the pull-down power MOSFET M5. The W-phase stator coil LW of themotor (MT) 1 is driven by the pull-up power MOSFET M3 and the pull-downpower MOSFET M6. The spindle output pre-driver 81 is driven by outputcontrol signals UPWM, UHIZ, VPWM, VHIZ, WPWM, WHIZ, which are generatedfrom the output drive controller 6A.

A motor drive current for the three-phase motor (MT) 1 is detected byusing the current detector 9A, which is formed by a DC shunt resistorRsns. One end of the DC shunt resistor Rsns is coupled to a commonsource of the three pull-down power MOSFETs M4, M5, M6 of the outputdriver 8 while the other end of the DC shunt resistor Rsns is coupled toa ground voltage. Therefore, the motor drive current I_(SENSE), whichflows to the common source of the three pull-down power MOSFETs M4, M5,M6 of the output driver 8, is converted to a voltage by the DC shuntresistor Rsns of the current detector 9A. The voltage is amplified bythe sense amplifier 9B. A current detection voltage CRNTOUT of the senseamplifier 9B is supplied to an A/D converter 4B through a selector 4A ofthe A/D conversion section 4. An error between a current detectiondigital signal at the output ADCOUT of the A/D converter 4B and acurrent instruction value supplied from the parameter setup register 7Ais calculated by the drive voltage generator 6C, and a drive voltageVDRV corresponding to the error is supplied from the output of the drivevoltage generator 6C to the input of the PWM modulator 6B. In responseto the drive voltage VDRV, the PWM modulator 6B supplies a PWM signal tothe input of the output drive controller 6A. Hence, the output drivecontroller 6A generates the output control signals UPWM, UHIZ, VPWM,VHIZ, WPWM, WHIZ, which PWM-drive the power MOSFETs of the output driver8. The current instruction value of the parameter setup register 7A canbe set, for instance, from a microcontroller external to the motor drivecontrol device shown in FIG. 13 through the serial port 7B.

Consequently, if the motor drive current I_(SENSE) detected by the DCshunt resistor Rsns of the current detector 9A is smaller than thecurrent instruction value of the parameter setup register 7A, the drivevoltage generator 6C is controlled so as to increase the VDRV signal atthe output of the drive voltage generator 6C. Hence, the duty of the PWMsignal at the output of the PWM modulator 6B increases to increase themotor drive current. If, on the contrary, the motor drive currentdetected by the DC shunt resistor Rsns of the current detector 9A isgreater than the current instruction value of the parameter setupregister 7A, the drive voltage generator 6C is controlled so as todecrease the VDRV signal at the output of the drive voltage generator6C. Hence, the duty of the PWM signal at the output of the PWM modulator6B decreases to decrease the motor drive current. In other words, thedifference between the motor drive current I_(SENSE) detected by thecurrent detector 9A and the current instruction value of the parametersetup register 7A is detected to adjust the duty of the PWM signal atthe output of the PWM modulator 6B until the difference decreases tozero. The output drive controller 6A then generates a PWM drive controlsignal for driving the power MOSFETs of the output driver 8 to controlthe motor drive current I_(SENSE).

The virtual midpoint generator 2 includes three resistors R_(U), R_(V),R_(W). One ends of the three resistors R_(U), R_(V), R_(W) are coupledto one ends of the stator coils LU, LV, LW of the motor (MT) 1. When theresistance values of the three resistors R_(U), R_(V), R_(W) of thevirtual midpoint generator 2 are set to the same resistance R, thevoltage at the other ends of the three resistors R_(U), R_(V), R_(W) isa virtual midpoint voltage that is substantially equal to the midpointpotential of the other end to which the U-phase stator coil LU, V-phasestator coil LV, and W-phase stator coil LW of the motor (MT) 1 arecommonly coupled.

The induced voltage detector 3 includes a selector 31, an amplifier 32,and a sample-and-hold circuit 33. The selector 31 includes a firstswitch SW1, a second switch SW2, and a third switch SW3. One end of thefirst switch SW1 is coupled to one end of the U-phase stator coil LU ofthe motor (MT) 1 and to one end of the resistor R_(U) of the virtualmidpoint generator 2. One end of the second switch SW2 is coupled to oneend of the V-phase stator coil LV of the motor (MT) 1 and to one end ofthe resistor R_(V) of the virtual midpoint generator 2. One end of thethird switch SW3 is coupled to one end of the W-phase stator coil LW ofthe motor (MT) 1 and to one end of the resistor R_(W) of the virtualmidpoint generator 2. The three other ends of the first, second, andthird switches SW1, SW2, SW3 of the selector 31 are commonly coupled toa noninverting input terminal+ of the amplifier 32. The virtual midpointvoltage at the other end to which the three resistors R_(U), R_(V),R_(W) of the virtual midpoint generator 2 are commonly coupled issupplied to an inverting input terminal− of the amplifier 32. Aselection signal SEL generated from an induced voltage determinationsection 51 of the initial acceleration controller 5 provides on/offcontrol of the first, second, and third switches SW1, SW2, SW3 of theselector 31. A signal output from the amplifier 32 of the inducedvoltage detector 3 is supplied to the input terminal of thesample-and-hold circuit 33. A detected induced voltage VMOUT, which is asample-and-hold output signal at the output terminal of thesample-and-hold circuit 33, is supplied to the A/D converter 4B throughthe selector 4A of the A/D conversion section 4.

The initial acceleration controller 5 includes the induced voltagedetermination section 51, a decoder 52, and a sequencer 53. The inducedvoltage determination section 51 determines the polarities of theinduced voltages of the U- and V- and W-phases of the motor (MT) 1,which are generated by the induced voltage detector 3 and the A/Dconversion section 4, and judges whether the induced voltages are higheror lower than a predetermined reference value V_(TH). The output of theinduced voltage determination section 51 generates an output signalDmode indicative of the pull-up and pull-down conducting phases of theU-, V-, and W-phases of the motor (MT) 1.

The decoder 52 in the initial acceleration controller 5 decodes theoutput signal Dmode, which is generated from the output of the inducedvoltage determination section 51, to generate initial accelerationoutput signals UPON, UNON, VPON, VNON, WPON, WNON specifying the pull-upand pull-down conducting phases of the U-, V-, and W-phases of the motor(MT) 1.

In response to a start signal Start for starting the rotation of thethree-phase motor (MT) 1, which is supplied from the parameter setupregister 7A, the sequencer 53 in the initial acceleration controller 5supplies a sense signal SENSE, which instructs the induced voltagedetector 3 to detect three-phase induced voltages, to the inducedvoltage determination section 51. Further, in response to the outputsignal Dmode, which is generated from the output of the induced voltagedetermination section 51, the sequencer 53 supplies to the inducedvoltage determination section 51 an initial acceleration conduction modesignal Smode indicative of a total of six conduction states, namely, theconduction states of the pull-up and pull-down conducting phases of theU-, V-, and W-phases of the motor (MT) 1.

In the motor drive control device studied by the inventors of thepresent invention before its disclosure, which is shown in FIG. 13, theconduction start phase is determined by identifying an initial rotorposition in accordance with the polarities of three-phase inducedvoltages, which are determined by the induced voltage detector 3, forinitial acceleration of the three-phase motor (MT) 1, as described inJapanese Unexamined Patent Publications No. 2006-115599 and 2008-113506.The determined conduction start phase is indicated by the output signalDmode indicative of a conducting phase, which is generated from theoutput terminal of the induced voltage determination section 51. Inaccordance with the result of determination of the conduction startphase, therefore, the motor drive control device shown in FIG. 13 beginsto conduct (for motor drive) and PWM-drive the three-phase motor (MT) 1.

While the three-phase motor (MT) 1 is PWM-driven by the motor drivecontrol device shown in FIG. 13, the induced voltage developed in anon-conducting phase is detected as described in Japanese UnexaminedPatent Publications No. 2006-115599 and 2008-113506. Further, the peakof the induced voltage is detected to change the conducting phase. Evenafter such a conducting phase change, the peak of the induced voltagedeveloped in a non-conducting phase during motor drive is continuouslydetected. The detected peak is then used to time a phase change for thepurpose of accelerating the motor.

However, as mentioned earlier, the inventors engaged in the developmenthave found that when the motor startup method adopted by the motor drivecontrol device shown in FIG. 13 is used, it is difficult to properlystart up various types of motors under operating conditions where motoroperations are performed in a wide range of temperature and power supplyvoltage.

FIGS. 14A and 14B are diagrams illustrating the dependence of an inducedvoltage developed in a non-conducting phase during PWM drive provided bythe motor drive control device studied by the inventors of the presentinvention before its disclosure, which is shown in FIG. 13, on a drivecurrent or on the duty of a PWM drive signal. The drive current and theduty of the PWM drive signal, which are shown in FIGS. 14A and 14B,respectively, are the drive current prevailing during PWM drive and theratio of a high-level period of the PWM drive signal, respectively.

The vertical axis of FIG. 14A represents an induced voltage that isdeveloped in a non-conducting phase during PWM drive while the duty ofthe PWM drive signal is placed under predetermined conditions. Thehorizontal axis of FIG. 14A represents a drive current prevailing duringPWM drive. As is obvious from FIG. 14A, the induced voltage increases inproportion to an increase in the drive current while the duty of the PWMdrive signal is placed under predetermined conditions.

The vertical axis of FIG. 14B represents an induced voltage that isdeveloped in a non-conducting phase during PWM drive while the drivecurrent prevailing during PWM drive is placed under predeterminedconditions. The horizontal axis of FIG. 14B represents the duty of thePWM drive signal. As is obvious from FIG. 14B, the induced voltagedecreases in inverse proportion to an increase in the duty of the PWMdrive signal (the ratio of a high-level period of the PWM drive signal).

When, in the motor drive control device shown in FIG. 13, conductionbegins after the initial rotor position is identified in accordance withthe determined polarities of three-phase induced voltages for initialacceleration, the drive current I_(SENSE) prevailing during PWM drivedecreases due, for instance, to an increase in the on-resistance of thepower MOSFETs M1-M6 of the output driver 8, which is caused by anabnormal decrease in a power supply voltage Vspn for the output driver 8and a temperature rise, and to the parasitic resistance provided by highresistance values of the stator coils LU, LV, LW of the motor (MT) 1.

Further, in the motor drive control device shown in FIG. 13, the motor(MT) 1 begins to rotate upon conduction (motor drive) for initialacceleration so that reverse voltages B-emf are developed acrosstwo-phase stator coils that are in conduction. As a result, the drivecurrent I_(SENSE) presently prevailing during PWM drive is calculated bysubtracting the voltage difference between the reverse voltages B-emf ofthe conducting two-phase stator coils from the power supply voltage Vspnof the output driver 8 and dividing the resulting voltage by the sum ofthe on-resistances of the power MOSFETs M1-M6 of the output driver 8 andthe parasitic resistances of the stator coils LU, LV, LW of the motor(MT) 1. As the voltage difference between the reverse voltages B-emf ofthe conducting two-phase stator coils increases when the motor (MT) 1accelerates, the drive current I_(SENSE) prevailing during PWM drive forinitial acceleration decreases.

For reasons described above, in the motor drive control device shown inFIG. 13, the drive current I_(SENSE) prevailing during PWM drive whichis provided at the beginning of conduction for initial acceleration issmaller than the current instruction value of the parameter setupregister 7A. Accordingly, as the motor drive current I_(SENSE) detectedby the current detector 9A is smaller than the current instruction valueof the parameter setup register 7A, the VDRV signal at the output of thedrive voltage generator 6C increases. This will increase the duty of thePWM signal at the output of the PWM modulator 6B, thereby increasing themotor drive current.

However, when the duty of the PWM drive signal increases, the inducedvoltage decreases in inverse proportion to an increase in the duty ofthe PWM drive signal as shown in FIG. 14B. Therefore, in the motor drivecontrol device studied by the inventors of the present invention beforeits disclosure, which is shown in FIG. 13, it is difficult for theinduced voltage determination section 51 to determine the polarities ofthe induced voltages developed in the U-, V-, and W-phases of the motor(MT) 1 and judge whether the induced voltages are higher or lower thanthe predetermined reference value V_(TH). Consequently, the studiesconducted by the inventors of the present invention before itsdisclosure have revealed that the output of the induced voltagedetermination section 51 does not generate the output signal Dmode,which indicates the pull-up and pull-down conducting phases of the U-,V-, and W-phases of the motor (MT) 1, thereby making it difficult toproperly start up the motor (MT) 1. Particularly, the parasiticresistances of the stator coils LU, LV, LW may be high depending on thetype of the motor (MT) 1, which is a three-phase DC motor. Therefore,even when the stator coils LU, LV, LW of the motor (MT) 1 have a highparasitic resistance, it is necessary to properly start up the motor(MT) 1.

The present invention has been made as a result of the above studiesconducted, for instance, by the inventors of the present inventionbefore its disclosure.

The present invention has been made in view of the above circumstancesto properly start up various types of motors under operating conditionswhere motor operations are performed in a wide range of temperature andpower supply voltage.

The foregoing and other advantages and novel features of the presentinvention will become apparent from the following description of thepresent invention and from the accompanying drawings.

A representative aspect of the present invention disclosed in thisdocument is outlined below.

According to the representative aspect of the present invention, thereis provided a motor drive control device including a voltage detector(3), an A/D conversion section (4), an initial acceleration controller(5), output drive controllers (6A, 6B, 6C), an output driver (8), and acurrent detector (9A).

The output driver (8) includes a plurality of power transistors (M1-M6)and an output pre-driver (81). The power transistors (M1-M6) drive amultiphase DC motor (1). The output pre-driver (81) drives a pluralityof input electrodes of the power transistors.

The current detector (9A) is capable of detecting a motor drive current(I_(SENSE)) that flows to the multiphase DC motor (1).

Detected information about the motor drive current, which is detected bythe current detector (9A), is converted to a current detection digitalsignal (ADCOUT) by the A/D conversion section (4).

The output drive controllers (6A, 6B, 6C) supply PWM drive outputsignals (UPWM, VPWM, WPWM) for PWM drive to the output pre-driver (81)in such a manner as to minimize the error between a current instructionsignal and the current detection digital signal (ADCOUT).

The voltage detector (3) is capable of detecting an induced voltagedeveloped across a stator coil (LU, LV, LW) of each phase of themultiphase DC motor (1) and generating a detected induced voltage(VMOUT).

When the multiphase DC motor (1) starts up, control is exercised toplace the initial acceleration controller (5) in an operating state. Inresponse to the detected induced voltage (VMOUT) generated from thevoltage detector (3), the initial acceleration controller (5) supplies aplurality of initial acceleration output signals (UPON, UNON, VPON,VNON, WPON, WNON) specifying a conducting phase for initial accelerationof the multiphase DC motor (1) to the output drive controllers (6A, 6B,6C).

The initial acceleration controller (5), the output drive controllers(6A, 6B, 6C), and the output driver (8) change the conducting phase andperform the PWM drive to provide the initial acceleration of themultiphase DC motor (1) in response to the detected induced voltage(VMOUT) and to the error upon startup of the multiphase DC motor (1).

Upper-limit duty values for the PWM drive output signals (UPWM, VPWM,WPWM) to be supplied from the output drive controllers (6A, 6B, 6C) tothe output pre-driver (81) during the period of the initial accelerationcan be arbitrarily set in the output drive controllers (6A, 6B, 6C) (seeFIG. 1).

An advantage provided by a representative aspect of the presentinvention is outlined below.

The present invention makes it possible to properly start up varioustypes of motors under operating conditions where motor operations areperformed in a wide range of temperature and power supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail basedon the following figures, in which:

FIG. 1 is a diagram illustrating the configuration of a motor drivecontrol device for driving a three-phase DC motor in accordance with afirst embodiment of the present invention;

FIGS. 2A and 2B are diagrams illustrating how a short pulse current, towhich a rotor does not respond, flows to field coils of two phases sothat an induced voltage will be detected by an induced voltage detector3, which identifies an initial rotor position of the three-phase motor(MT) 1 before its initial acceleration in the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1;

FIG. 3 is a diagram illustrating the waveforms of reverse voltagesB-emf(U), B-emf(V), B-emf(W) developed across stator coils LU, LV, LW ofthe three-phase motor (MT) 1 due to its rotation in the motor drivecontrol device according to the first embodiment, which is shown in FIG.1;

FIG. 4 is a diagram that relates to the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1, andillustrates the waveform of a normalized induced voltage derived fromthe sum of an induced voltage Vm+ developed in a non-conducting U-phaseby the conduction of a forward-direction short pulse current shown inFIG. 2A and an induced voltage Vm− developed in the non-conductingU-phase by the conduction of a reverse-direction short pulse currentshown in FIG. 2B;

FIG. 5 is a diagram illustrating the configuration of an induced voltagedetermination section 51 in an initial acceleration controller 5 of themotor drive control device according to the first embodiment, which isshown in FIG. 1;

FIG. 6 is a diagram that relates to the motor drive control deviceaccording to the first embodiment, which is shown in FIGS. 1 and 5, andillustrates the waveforms of reverse voltages B-emf(U), B-emf(V),B-emf(W) of three-phase stator coils LU, LV, LW of the motor (MT) 1,three-phase added induced voltages (Vmu+)+(Vmu−), (Vmv+)+(Vmv−),(Vmw+)+(Vmw−), and an absolute value output ADCOUT of an absolute valuecircuit 514;

FIG. 7 is a diagram illustrating the configuration of a drive voltagegenerator 6C in the motor drive control device according to the firstembodiment, which is shown in FIG. 1;

FIG. 8 is a diagram illustrating the configuration of a PWM modulator 6Band of an output drive controller 6A that prevails at the beginning ofconduction for initial acceleration in the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1;

FIG. 9 is a waveform diagram illustrating how the PWM modulator 6B andthe output drive controller 6A operate at the beginning of conductionfor initial acceleration in the motor drive control device according tothe first embodiment, which is shown in FIG. 8;

FIG. 10 is an operating sequence diagram illustrating a rotor positionidentification operation based on a three-phase sense and a conductingoperation for initial acceleration, which are performed by the motordrive control device according to the first embodiment, which is shownin FIGS. 1 and 7;

FIG. 11 is a diagram illustrating the configuration of the inducedvoltage determination section 51 in the initial acceleration controller5 of the motor drive control device according to a second embodiment ofthe present invention;

FIG. 12 is a diagram that relates to the motor drive control deviceincluding the induced voltage determination section 51 according to thesecond embodiment, which is shown in FIG. 11, and illustrates thewaveforms of the reverse voltages of three-phase stator coils LU, LV, LWof the motor (MT) 1, the waveforms of the three-phase added inducedvoltages, the waveform of the absolute value output ADCOUT of theabsolute value circuit 514, the waveform of a comparator output signalCOM, and the waveform of a polarity determination signal POL;

FIG. 13 is a diagram illustrating the configuration of a motor drivecontrol device for driving a three-phase DC motor, which has beenstudied by the inventors of the present invention before its disclosure;and

FIGS. 14A and 14B are diagrams illustrating the dependence of an inducedvoltage developed in a non-conducting phase during PWM drive provided bythe motor drive control device studied by the inventors of the presentinvention before its disclosure, which is shown in FIG. 13, on a drivecurrent or on the duty of a PWM drive signal.

DETAILED DESCRIPTION 1. Overview of Embodiments

First of all, embodiments representative of the present inventiondisclosed in this document will be summarized. The parenthesizedreference numerals in the accompanying drawings referred to in theoverview of the representative embodiments merely illustrate what iscontained in the concept of elements to which the reference numerals areaffixed.

[1] According to a representative aspect of the present invention, thereis provided a motor drive control device including a voltage detector(3), an A/D conversion section (4), an initial acceleration controller(5), output drive controllers (6A, 6B, 6C), an output driver (8), and acurrent detector (9A).

The output driver (8) includes a plurality of power transistors (M1-M6)and an output pre-driver (81). The power transistors (M1-M6) drive amultiphase DC motor (1). The output pre-driver (81) drives a pluralityof input electrodes of the power transistors.

The current detector (9A) is capable of detecting a motor drive current(I_(SENSE)) that flows to the multiphase DC motor (1).

Detected information about the motor drive current, which is detected bythe current detector (9A), is converted to a current detection digitalsignal (ADCOUT) by the A/D conversion section (4).

The output drive controllers (6A, 6B, 6C) supply PWM drive outputsignals (UPWM, VPWM, WPWM) for PWM drive to the output pre-driver (81)in such a manner as to minimize the error between a current instructionsignal and the current detection digital signal (ADCOUT).

The voltage detector (3) is capable of detecting the induced voltagedeveloped across the stator coil (LU, LV, LW) of each phase of themultiphase DC motor (1) and generating a detected induced voltage(VMOUT).

When the multiphase DC motor (1) starts up, control is exercised toplace the initial acceleration controller (5) in an operating state. Inresponse to the detected induced voltage (VMOUT) generated from thevoltage detector (3), the initial acceleration controller (5) supplies aplurality of initial acceleration output signals (UPON, UNON, VPON,VNON, WPON, WNON) specifying a conducting phase for initial accelerationof the multiphase DC motor (1) to the output drive controllers (6A, 6B,6C).

The initial acceleration controller (5), the output drive controllers(6A, 6B, 6C), and the output driver (8) change the conducting phase andperform the PWM drive to provide the initial acceleration of themultiphase DC motor (1) in response to the detected induced voltage(VMOUT) and to the error upon startup of the multiphase DC motor (1).

Upper-limit duty values for the PWM drive output signals (UPWM, VPWM,WPWM) to be supplied from the output drive controllers (6A, 6B, 6C) tothe output pre-driver (81) during the period of the initial accelerationcan be arbitrarily set in the output drive controllers (6A, 6B, 6C) (seeFIG. 1).

According to the above aspect of the present invention, various types ofmotors can be properly started up under operating conditions where motoroperations are performed in a wide range of temperature and power supplyvoltage.

In a preferred aspect of the present invention, the detected inducedvoltage (VMOUT), which is generated from the voltage detector (3), isconverted to an induced voltage detection digital signal (ADCOUT) by theA/D conversion section (4).

Before the initial acceleration, the initial acceleration controller (5)can identify the position of a rotor of the multiphase DC motor (1) froma combination of pieces of polarity information carried by the inducedvoltage detection digital signal (ADCOUT) concerning the phases of themultiphase DC motor (1) (see FIG. 6).

In another preferred aspect of the present invention, the initialacceleration controller (5) determines a first conducting phase for theinitial acceleration in accordance with the rotor position identifiedbefore the initial acceleration (see FIG. 6).

In still another preferred aspect of the present invention, the initialacceleration controller (5) makes the conducting phase change when theinduced voltage detection digital signal (ADCOUT) reaches apredetermined reference value (V_(TH)) after the energization of thefirst conducting phase for the initial acceleration (see FIG. 6).

In a more preferred aspect of the present invention, the motor drivecontrol device further includes input circuits (7A, 7B) capable ofreceiving a control signal from the outside of the motor drive controldevice.

A duty control signal (CLPWM), which is used to arbitrarily set theupper-limit duty values for the PWM drive output signals (UPWM, VPWM,WPWM) to be supplied from the output drive controllers (6A, 6B, 6C) tothe output pre-driver (81) during the period of the initialacceleration, can be supplied from the outside of the motor drivecontrol device to the output drive controllers (6A, 6B, 6C) through theinput circuits (7A, 7B) (see FIG. 1).

In another more preferred aspect of the present invention, the initialacceleration controller (5) generates a clamp enable signal (CLENA)during the period of the initial acceleration in response to a startsignal (Start) for starting the rotation of the multiphase DC motor (1),which is supplied from the input circuits (7A, 7B).

During the period of the initial acceleration, in response to the clampenable signal (CLENA) generated from the initial acceleration controller(5), the output drive controllers (6A, 6B, 6C) set the upper-limit dutyvalues for the PWM drive output signals (UPWM, VPWM, WPWM), which are tobe supplied to the output pre-driver (81), in accordance with the dutycontrol signal (CLPWM) (see FIGS. 1 and 7).

In still another more preferred aspect of the present invention, theinitial acceleration controller (5) detects that the induced voltagedetection digital signal (ADCOUT) has not reached the predeterminedreference value (V_(TH)) at a predetermined timing, and then generates adetection signal (COM), which indicates that the predetermined referencevalue (V_(TH)) is not reached.

In response to the detection signal (COM), which indicates that thepredetermined reference value (V_(TH)) is not reached, the initialacceleration controller (5) generates a low-level sub-reference value(V_(THSUB)) that is lower than the predetermined reference value(V_(TH)).

When the induced voltage detection digital signal (ADCOUT) reaches thelow-level sub-reference value (V_(THSUB)), the initial accelerationcontroller (5) makes the conducting phase change (see FIGS. 11 and 12).

In yet another more preferred aspect of the present invention, thepredetermined reference value (V_(TH)) can be supplied from the outsideof the motor drive control device to the initial acceleration controller(5) through the input circuits (7A, 7B) (see FIG. 1).

In a detailed aspect of the present invention, the voltage detector (3),the A/D conversion section (4), the initial acceleration controller (5),the output drive controllers (6A, 6B, 6C), and the output driver (8) areintegrated in a semiconductor chip having a semiconductor integratedcircuit (see FIG. 1).

In the most detailed aspect of the present invention, the voltagedetector (3), the A/D conversion section (4), the initial accelerationcontroller (5), the output drive controllers (6A, 6B, 6C), and theoutput driver (8), which are integrated in the semiconductor chip havingthe semiconductor integrated circuit, are capable of driving themultiphase DC motor (1), which is a three-phase DC motor serving as aspindle motor for rotating a magnetic disk in a hard disk drive (seeFIG. 1).

[2] According to another representative aspect of the present invention,there is provided a method of operating a motor drive control devicethat includes a voltage detector (3), an A/D conversion section (4), aninitial acceleration controller (5), output drive controllers (6A, 6B,6C), an output driver (8), and a current detector (9A).

The output driver (8) includes a plurality of power transistors (M1-M6)and an output pre-driver (81). The power transistors (M1-M6) drive amultiphase DC motor (1). The output pre-driver (81) drives a pluralityof input electrodes of the power transistors.

The current detector (9A) is capable of detecting a motor drive current(I_(SENSE)) that flows to the multiphase DC motor (1).

Detected information about the motor drive current, which is detected bythe current detector (9A), is converted to a current detection digitalsignal (ADCOUT) by the A/D conversion section (4).

The output drive controllers (6A, 6B, 6C) supply PWM drive outputsignals (UPWM, VPWM, WPWM) for PWM drive to the output pre-driver (81)in such a manner as to minimize the error between a current instructionsignal and the current detection digital signal (ADCOUT).

The voltage detector (3) is capable of detecting the induced voltagedeveloped across the stator coil (LU, LV, LW) of each phase of themultiphase DC motor (1) and generating a detected induced voltage(VMOUT).

When the multiphase DC motor (1) starts up, control is exercised toplace the initial acceleration controller (5) in an operating state. Inresponse to the detected induced voltage (VMOUT) generated from thevoltage detector (3), the initial acceleration controller (5) supplies aplurality of initial acceleration output signals (UPON, UNON, VPON,VNON, WPON, WNON) specifying a conducting phase for initial accelerationof the multiphase DC motor (1) to the output drive controllers (6A, 6B,6C).

The initial acceleration controller (5), the output drive controllers(6A, 6B, 6C), and the output driver (8) change the conducting phase andperform the PWM drive to provide the initial acceleration of themultiphase DC motor (1) in response to the detected induced voltage(VMOUT) and to the error upon startup of the multiphase DC motor (1).

Upper-limit duty values for the PWM drive output signals (UPWM, VPWM,WPWM) to be supplied from the output drive controllers (6A, 6B, 6C) tothe output pre-driver (81) during the period of the initial accelerationcan be arbitrarily set in the output drive controllers (6A, 6B, 6C) (seeFIG. 1).

According to the above-described aspects of the present invention,various types of motors can be properly started up under operatingconditions where motor operations are performed in a wide range oftemperature and power supply voltage.

2. Details of Embodiments

Embodiments of the present invention will now be described in furtherdetail. Throughout the drawings for illustrating the best embodimentsfor implementing the present invention, parts having the same functionsare designated by the same reference numerals and will not beredundantly described.

First Embodiment Essential Configuration of Motor Drive Control Device

FIG. 1 is a diagram illustrating the configuration of a motor drivecontrol device for driving a three-phase DC motor in accordance with afirst embodiment of the present invention.

Essential differences between the motor drive control device accordingto the first embodiment of the present invention, which is shown in FIG.1, and the motor drive control device studied by the inventors of thepresent invention before its disclosure, which is shown in FIG. 13, aredescribed below.

In the motor drive control device according to the first embodiment,which is shown in FIG. 1, the sequencer 53 in the initial accelerationcontroller 5 supplies a clamp enable signal CLENA to a drive voltagegenerator 6C, and a parameter setup register 7A supplies a PWM dutyupper-limit clamp signal CLPWM to the drive voltage generator 6C.

The clamp enable signal CLENA makes it possible to clamp an increase inthe duties of PWM drive control signals UPWM, VPWM, WPWM, which aregenerated from an output drive controller 6A when conduction starts forinitial acceleration after an initial rotor position is identified by aninduced voltage detector 3. The PWM duty upper-limit clamp signal CLPWMsets a PWM duty upper-limit value for a duty clamp operation on the PWMdrive control signals UPWM, VPWM, WPWM, which is enabled by the clampenable signal CLENA. This upper-limit setting to be specified by the PWMduty upper-limit clamp signal CLPWM can be arbitrarily defined from anexternal microcontroller or central processing unit (CPU) through aserial port 7B. Further, the clamp enable signal CLENA is kept at a highlevel by the sequencer 53 in the initial acceleration controller 5during a delay time, which corresponds to an initial acceleration periodsubsequent to a low-to-high level change in a later-described startsignal Start. At the end of the delay time, which corresponds to theinitial acceleration period, the sequencer 53 in the initialacceleration controller 5 changes the level of the clamp enable signalCLENA from high to low.

It is therefore assumed that a high-level clamp enable signal CLENA issupplied from the sequencer 53 in the initial acceleration controller 5to the drive voltage generator 6C, and that a PWM duty upper-limit clampsignal CLPWM indicating a PWM duty upper-limit value, for instance, of80% is supplied from the parameter setup register 7A to the drivevoltage generator 6C. The error between a current detection digitalsignal at the output ADCOUT of an A/D converter 4B and a currentinstruction value supplied from the parameter setup register 7A iscalculated by the drive voltage generator 6C. A drive voltage VDRVequivalent to 80% of the maximum value of this error is supplied fromthe output of the drive voltage generator 6C to the input of a PWMmodulator 6B. In response to the drive voltage VDRV equivalent to 80% ofthe maximum error, the PWM modulator 6B supplies a PWM signal whosemaximum voltage amplitude is limited to 80% to the input of the outputdrive controller 6A. Therefore, the upper limit on an increase in theduties of the PWM drive control signals UPWM, VPWM, WPWM generated fromthe output drive controller 6A is clamped at 80% as specified by the PWMduty upper-limit clamp signal CLPWM.

Consequently, the motor drive control device according to the firstembodiment, which is shown in FIG. 1, also clamps a decrease in theinduced voltage because an increase in the duty of a PWM drive signalshown in FIG. 14B is clamped at 80% as specified by the PWM dutyupper-limit clamp signal CLPWM.

As a result, even when the PWM drive current I_(SENSE) prevailing duringinitial acceleration is smaller than the current instruction valuesupplied from the parameter setup register 7A due, for instance, to highparasitic resistances of stator coils LU, LV, LW of a motor (MT) 1, aninduced voltage determination section 51 can determine the polarities ofinduced voltages in the U-, V-, and W-phases of the motor (MT) 1 andjudge whether the induced voltages are higher or lower than thepredetermined reference value V_(TH). Therefore, the output of theinduced voltage determination section 51 generates an output signalDmode, which indicates the pull-up and pull-down conducting phases ofthe U-, V-, and W-phases of the motor (MT) 1. This makes it possible toproperly start up the motor (MT) 1.

The configuration of the motor drive control device according to thefirst embodiment, which is shown in FIG. 1, will now be described indetail.

<Detailed Configuration of Motor Drive Control Device>

As shown in FIG. 1, voltage sources, which equivalently exhibit reversevoltages B-emf (U), B-emf (V), B-emf (W), are coupled to one ends ofstator coils of the motor (MT) 1, namely, a U-phase stator coil LU, aV-phase stator coil LV, and a W-phase stator coil LW. The other ends ofthe U-phase stator coil LU, V-phase stator coil LV, and W-phase statorcoil LW of the motor (MT) 1 are commonly coupled as a midpoint.

The motor drive control device shown in FIG. 1 includes a virtualmidpoint generator 2, an induced voltage detector 3, an A/D conversionsection 4, an initial acceleration controller 5, an output drivecontroller 6A, a PWM modulator 6B, a drive voltage generator 6C, aparameter setup register 7A, a serial port 7B, an output driver 8, acurrent detector 9A, and a sense amplifier 9B.

In the motor drive control device shown in FIG. 1, components other thanthe current detector 9A, namely, the virtual midpoint generator 2, theinduced voltage detector 3, the A/D conversion section 4, the initialacceleration controller 5, the output drive controller 6A, the PWMmodulator 6B, the drive voltage generator 6C, the parameter setupregister 7A, the serial port 7B, the output driver 8, and the senseamplifier 9B, are integrated in a semiconductor chip having asemiconductor integrated circuit called a motor driver IC. The motordrive control device, which is shown in FIG. 1 and formed by thesemiconductor integrated circuit called the motor driver IC, drives athree-phase motor (MT) 1, which is a three-phase DC motor serving as aspindle motor for rotating a magnetic disk in a hard disk drive (HDD).

<Output Driver>

The stator coils LU, LV, LW of the three-phase motor (MT) 1 arePWM-driven by the output driver 8. The output driver 8 includes aspindle output pre-driver 81, pull-up power MOSFETs M1, M2, M3, andpull-down power MOSFETs M4, M5, M6. The U-phase stator coil LU of themotor (MT) 1 is driven by the pull-up power MOSFET M1 and pull-downpower MOSFET M4. The V-phase stator coil LV of the motor (MT) 1 isdriven by the pull-up power MOSFET M2 and pull-down power MOSFET M5. TheW-phase stator coil LW of the motor (MT) 1 is driven by the pull-uppower MOSFET M3 and pull-down power MOSFET M6. The spindle outputpre-driver 81 is driven by output control signals UPWM, UHIZ, VPWM,VHIZ, WPWM, WHIZ, which are generated from the output drive controller6A.

<Current Detector and Sense Amplifier>

A motor drive current for the three-phase motor (MT) 1 is detected byusing the current detector 9A, which is formed by a DC shunt resistorRsns. One end of the DC shunt resistor Rsns is coupled to a commonsource of the three pull-down power MOSFETs M4, M5, M6 of the outputdriver 8 while the other end of the DC shunt resistor Rsns is coupled toa ground voltage.

Therefore, the motor drive current I_(SENSE), which flows to the commonsource of the three pull-down power MOSFETs M4, M5, M6 of the outputdriver 8, is converted to a voltage by the DC shunt resistor Rsns of thecurrent detector 9A. The voltage is amplified by the sense amplifier 9B.A current detection voltage CRNTOUT of the sense amplifier 9B issupplied to an A/D converter 4B through a selector 4A of the A/Dconversion section 4.

<Drive Voltage Generator, PWM Modulator, and Output Drive Controller>

An error between a current detection digital signal at the output ADCOUTof the A/D converter 4B and a current instruction value supplied fromthe parameter setup register 7A is calculated by the drive voltagegenerator 6C, and a drive voltage VDRV corresponding to the error issupplied from the output of the drive voltage generator 6C to the inputof the PWM modulator 6B. In response to the drive voltage VDRV, the PWMmodulator 6B supplies a PWM signal to the input terminal of the outputdrive controller 6A. Hence, the output drive controller 6A generates theoutput control signals UPWM, UHIZ, VPWM, VHIZ, WPWM, WHIZ, whichPWM-drive the power MOSFETs of the output driver 8. The currentinstruction value of the parameter setup register 7A can be set, forinstance, from a microcontroller external to the motor drive controldevice shown in FIG. 13 through the serial port 7B. Further, thepredetermined reference value V_(TH), which is set in the inducedvoltage determination section 51 of the initial acceleration controller5 from the parameter setup register 7A for a conducting phase change,can also be set in the parameter setup register 7A, for instance, from amicrocontroller external to the motor drive control device shown in FIG.1 through the serial port 7B.

Consequently, if the motor drive current I_(SENSE) detected by the DCshunt resistor Rsns of the current detector 9A is smaller than thecurrent instruction value of the parameter setup register 7A, the drivevoltage generator 6C is controlled so as to increase the VDRV signal atthe output of the drive voltage generator 6C. Hence, the duty of the PWMsignal at the output of the PWM modulator 6B increases to increase themotor drive current. If, on the contrary, the motor drive currentdetected by the DC shunt resistor Rsns of the current detector 9A isgreater than the current instruction value of the parameter setupregister 7A, the drive voltage generator 6C is controlled so as todecrease the VDRV signal at the output of the drive voltage generator6C. Hence, the duty of the PWM signal at the output of the PWM modulator6B decreases to decrease the motor drive current. In other words, thedifference between the motor drive current I_(SENSE) detected by thecurrent detector 9A and the current instruction value of the parametersetup register 7A is detected to adjust the duty of the PWM signal atthe output of the PWM modulator 6B until the difference decreases tozero. The output drive controller 6A then generates a PWM drive controlsignal for driving the power MOSFETs of the output driver 8 to controlthe motor drive current I_(SENSE).

<Virtual Midpoint Generator>

The virtual midpoint generator 2 includes three resistors R_(U), R_(V),R_(W). One ends of the three resistors R_(U), R_(V), R_(W) are coupledto one ends of the stator coils LU, LV, LW of the motor (MT) 1. When theresistance values of the three resistors R_(U), R_(V), R_(W) of thevirtual midpoint generator 2 are set to the same resistance R, thevoltage at the other ends of the three resistors R_(U), R_(V), R_(W) isa virtual midpoint voltage that is substantially equal to the midpointpotential of the other end to which the U-phase stator coil LU, V-phasestator coil LV, and W-phase stator coil LW of the motor (MT) 1 arecommonly coupled.

<Induced Voltage Detector and A/D Conversion Section>

The induced voltage detector 3 includes a selector 31, an amplifier 32,and a sample-and-hold circuit 33. The selector 31 includes a firstswitch SW1, a second switch SW2, and a third switch SW3. One end of thefirst switch SW1 is coupled to one end of the U-phase stator coil LU ofthe motor (MT) 1 and to one end of the resistor R_(U) of the virtualmidpoint generator 2. One end of the second switch SW2 is coupled to oneend of the V-phase stator coil LV of the motor (MT) 1 and to one end ofthe resistor R_(V) of the virtual midpoint generator 2. One end of thethird switch SW3 is coupled to one end of the W-phase stator coil LW ofthe motor (MT) 1 and to one end of the resistor R_(W) of the virtualmidpoint generator 2. The three other ends of the first, second, andthird switches SW1, SW2, SW3 of the selector 31 are commonly coupled toa noninverting input terminal+ of the amplifier 32. The virtual midpointvoltage at the other end to which the three resistors R_(U), R_(V),R_(W) of the virtual midpoint generator 2 are commonly coupled issupplied to an inverting input terminal− of the amplifier 32. Aselection signal SEL generated from the induced voltage determinationsection 51 of the initial acceleration controller 5 provides on/offcontrol of the first, second, and third switches SW1, SW2, SW3 of theselector 31. A signal output from the amplifier 32 of the inducedvoltage detector 3 is supplied to the input terminal of thesample-and-hold circuit 33. A detected induced voltage VMOUT, which is asample-and-hold output signal at the output terminal of thesample-and-hold circuit 33, is supplied to the A/D converter 4B throughthe selector 4A of the A/D conversion section 4.

<Initial Acceleration Controller>

The initial acceleration controller 5 includes the induced voltagedetermination section 51, a decoder 52, and the sequencer 53. Theinduced voltage determination section 51 determines the polarities ofthe induced voltages in the U-, V-, and W-phases of the motor (MT) 1,which are generated by the induced voltage detector 3 and the A/Dconversion section 4, and judges whether the induced voltages are higheror lower than the predetermined reference value V_(TH). The output ofthe induced voltage determination section 51 generates the output signalDmode, which indicates the pull-up and pull-down conducting phases ofthe U-, V-, and W-phases of the motor (MT) 1.

The decoder 52 in the initial acceleration controller 5 decodes theoutput signal Dmode, which is generated from the output of the inducedvoltage determination section 51, to generate initial accelerationoutput signals UPON, UNON, VPON, VNON, WPON, WNON specifying the pull-upand pull-down conducting phases of the U-, V-, and W-phases of the motor(MT) 1.

In response to a start signal Start for starting the rotation of thethree-phase motor (MT) 1, which is supplied from the parameter setupregister 7A, the sequencer 53 in the initial acceleration controller 5supplies a sense signal SENSE, which instructs the induced voltagedetector 3 to detect three-phase induced voltages, to the inducedvoltage determination section 51. Further, in response to the outputsignal Dmode, which is generated from the output of the induced voltagedetermination section 51, the sequencer 53 supplies to the inducedvoltage determination section 51 an initial acceleration conduction modesignal Smode indicative of a total of six conduction states, namely, theconduction states of the pull-up and pull-down conducting phases of theU-, V-, and W-phases of the motor (MT) 1.

In the motor drive control device according to the first embodiment,which is shown in FIG. 1, a conduction start phase is determined byidentifying the initial rotor position for initial acceleration of thethree-phase motor (MT) 1 in accordance with the polarities ofthree-phase induced voltages, which are determined by the inducedvoltage detector 3, as described in Japanese Unexamined PatentPublications No. 2006-115599 and 2008-113506. The determined conductionstart phase is indicated by the output signal Dmode indicative of aconducting phase, which is generated from the output terminal of theinduced voltage determination section 51. Therefore, in response to theresult of determination of the conduction start phase, the motor drivecontrol device according to the first embodiment, which is shown in FIG.1, begins to conduct (for motor drive) and PWM-drive the three-phasemotor (MT) 1.

While PWM drive is being provided by the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1, an inducedvoltage developed in a non-conducting phase is detected as described inJapanese Unexamined Patent Publication No. 2008-113506 to make aconducting phase change when the induced voltage exceeds thepredetermined reference value V_(TH). Further, even after such aconducting phase change, a timing at which an induced voltage developedin a non-conducting phase during motor drive exceeds the predeterminedreference value V_(TH) is continuously detected. The motor is thenaccelerated by using the detected timing as the timing for a phasechange.

<Detection of Induced Voltage>

FIGS. 2A and 2B are diagrams illustrating how a short pulse current, towhich a rotor does not respond, flows to field coils of two phases sothat an induced voltage will be detected by the induced voltage detector3, which identifies the initial rotor position of the three-phase motor(MT) 1 for its initial acceleration in the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1.

FIG. 2A is a diagram illustrating how an induced voltage Vm+, which isdependent on the positional relationship between a rotor's magnet and astator's field coil, is developed in a non-conducting U-phase when ashort pulse current flows in a forward direction from the V-phase of themotor (MT) 1 to the W-phase.

FIG. 2B is a diagram illustrating how an induced voltage Vm−, which isdependent on the positional relationship between the rotor's magnet andthe stator's field coil, is generated in a non-conducting U-phase when ashort pulse current flows in a reverse direction from the W-phase of themotor (MT) 1 to the V-phase.

<Reverse Voltage>

FIG. 3 is a diagram illustrating the waveforms of the reverse voltagesB-emf(U), B-emf(V), B-emf(W) developed across the stator coils LU, LV,LW of the three-phase motor (MT) 1 due to its rotation in the motordrive control device according to the first embodiment, which is shownin FIG. 1.

The reverse voltage B-emf(U) developed across the stator coil LU isindicated by a line with solid circles. The reverse voltage B-emf(V)developed across the stator coil LV is indicated by a line with solidsquares. The reverse voltage B-emf(W) developed across the stator coilLW is indicated by a line with solid triangles.

<Total Normalized Induced Voltage>

FIG. 4 is a diagram that relates to the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1, andillustrates the waveform of a normalized induced voltage derived fromthe sum of the induced voltage Vm+ developed in a non-conducting U-phaseby the conduction of a forward-direction short pulse current shown inFIG. 2A and an induced voltage Vm− developed in the non-conductingU-phase by the conduction of a reverse-direction short pulse currentshown in FIG. 2B.

Referring to FIG. 4, the induced voltage Vm+ developed in thenon-conducting U-phase by the conduction of the forward-direction shortpulse current shown in FIG. 2A is indicated by a line with solidsquares; the induced voltage Vm− developed in the non-conducting U-phaseby the conduction of the reverse-direction short pulse current shown inFIG. 2B is indicated by a line with blank triangles; and the normalizedinduced voltage derived from the sum of the induced voltage Vm+ andinduced voltage Vm− is indicated by a thick solid line. The polarity ofthe normalized induced voltage indicated by the thick solid line in FIG.4 changes at intervals of an electrical angle of 180 degrees. Hence, thephase of the normalized induced voltage developed in the non-conductingU-phase, which is indicated by the thick solid line in FIG. 4, isadvanced by an electrical angle of 90 degrees from the phase of thereverse voltage B-emf(U) developed in the stator coil LU, which isindicated by the line with solid circles in FIG. 3.

<Induced Voltage Determination Section>

FIG. 5 is a diagram illustrating the configuration of the inducedvoltage determination section 51 in the initial acceleration controller5 of the motor drive control device according to the first embodiment,which is shown in FIG. 1.

As shown in FIG. 5, the induced voltage determination section 51includes a sense phase decoder 511, an induced voltage storage register512, an addition section 513, an absolute value circuit 514, acomparator 515, and a conducting phase decoder 516.

In response to the sense signal SENSE, which is supplied from thesequencer 53 shown in FIG. 1 to specify an operation of detectinginduced voltages of three phases, and to the initial accelerationconduction mode signal Smode, which indicates a total of six conductionstates, namely, the conduction states of the pull-up and pull-downconducting phases of the U-, V-, and W-phases of the motor (MT) 1, thesense phase decoder 511 generates six storage enable signals en, whichare to be supplied to the induced voltage storage register 512.

The output ADCOUT of the A/D converter 4B in the A/D conversion section4 shown in FIG. 1 supplies an induced voltage digital conversion signalto six registers (first to sixth registers) 5121-5126 of the inducedvoltage storage register 512 and to the input terminal of the absolutevalue circuit 514.

At a timing at which the sense phase decoder 511 generates a firststorage enable signal en, the first register 5121 stores a digitalconversion signal of an induced voltage Vmu+, which is developed in anon-conducting U-phase by a short pulse current flowing in a forwarddirection from the V-phase of the motor (MT) 1 to the W-phase. At atiming at which the sense phase decoder 511 generates a second storageenable signal en, the second register 5122 stores a digital conversionsignal of an induced voltage Vmu−, which is developed in thenon-conducting U-phase by a short pulse current flowing in a reversedirection from the W-phase of the motor (MT) 1 to the V-phase.

At a timing at which the sense phase decoder 511 generates a thirdstorage enable signal en, the third register 5123 stores a digitalconversion signal of an induced voltage Vmv+, which is developed in anon-conducting V-phase by a short pulse current flowing in a forwarddirection from the U-phase of the motor (MT) 1 to the W-phase. At atiming at which the sense phase decoder 511 generates a fourth storageenable signal en, the fourth register 5124 stores a digital conversionsignal of an induced voltage Vmv−, which is developed in thenon-conducting V-phase by a short pulse current flowing in a reversedirection from the W-phase of the motor (MT) 1 to the U-phase.

At a timing at which the sense phase decoder 511 generates a fifthstorage enable signal en, the fifth register 5125 stores a digitalconversion signal of an induced voltage Vmw+, which is developed in anon-conducting W-phase by a short pulse current flowing in a forwarddirection from the U-phase of the motor (MT) 1 to the V-phase. At atiming at which the sense phase decoder 511 generates a sixth storageenable signal en, the sixth register 5126 stores a digital conversionsignal of an induced voltage Vmw−, which is developed in thenon-conducting W-phase by a short pulse current flowing in a reversedirection from the V-phase of the motor (MT) 1 to the U-phase.

The addition section 513 includes a first adder 5131, a second adder5132, and a third adder 5133.

The first adder 5131 generates an added induced voltage (Vmu+)+(Vmu−)digital conversion signal by adding the induced voltage Vmu+ digitalconversion signal, which is information stored in the first register5121, to the induced voltage Vmu− digital conversion signal, which isinformation stored in the second register 5122.

The second adder 5132 generates an added induced voltage (Vmv+)+(Vmv−)digital conversion signal by adding the induced voltage Vmv+ digitalconversion signal, which is information stored in the third register5123, to the induced voltage Vmv− digital conversion signal, which isinformation stored in the fourth register 5124.

The third adder 5133 generates an added induced voltage (Vmw+)+(Vmw−)digital conversion signal by adding the induced voltage Vmw+ digitalconversion signal, which is information stored in the fifth register5125, to the induced voltage Vmw− digital conversion signal, which isinformation stored in the sixth register 5126.

The absolute value of the induced voltage digital conversion signal atthe output ADCOUT of the A/D converter 4B, which is generated at theoutput terminal of the absolute value circuit 514, and the digitalequivalent of the predetermined reference value V_(TH) supplied from theparameter setup register 7A shown in FIG. 1 are compared by thecomparator 515. A resulting comparator output signal COM is supplied tothe conducting phase decoder 516.

The conducting phase decoder 516 generates the conducting phaseindication output signal Dmode in response to the sense signal SENSEindicative of an operation performed to detect induced voltages of threephases, to the digital conversion signals (Vmu+)+(Vmu−), (Vmv+)+(Vmv−),(Vmw+)+(Vmw−) from the addition section 513, to the initial accelerationconduction mode signal Smode indicative of six conduction states, and tothe comparator output signal COM of the comparator 515. Hence, theconducting phase decoder 516 determines the polarities of the addedinduced voltages of the U-, V-, and W-phases of the motor (MT) 1, whichare generated by the induced voltage detector 3 and by the A/Dconversion section 4, and judges whether the added induced voltages arehigher or lower than the predetermined reference value V_(TH). In thismanner, the induced voltage determination section 51 generates theoutput signal Dmode, which indicates the pull-up and pull-downconducting phases of the U-, V-, and W-phases of the motor (MT) 1.

<Rotor Position Identification>

FIG. 6 is a diagram that relates to the motor drive control deviceaccording to the first embodiment, which is shown in FIGS. 1 and 5, andillustrates the waveforms of reverse voltages B-emf(U), B-emf(V),B-emf(W) of three-phase stator coils LU, LV, LW of the motor (MT) 1,three-phase added induced voltages (Vmu+)+(Vmu−), (Vmv+)+(Vmv−),(Vmw+)+(Vmw−), and an absolute value output ADCOUT of the absolute valuecircuit 514.

As shown in the table at the bottom of FIG. 6, the rotor position can beidentified in steps of 60 degrees of electrical angle from a combinationof pieces of polarity information (positive/negative) about the addedinduced voltages of three phases. When, for instance, the polarities ofthe added induced voltages of the U-, V- and W-phases are positive,positive, and negative, respectively, the rotor is found to be at anelectrical angle between 0 and 60 degrees. In this instance, allowing adrive current to flow from the U-phase to the V-phase makes it possibleto generate a normal rotation torque and rotate the rotor in a normaldirection.

As described earlier, the conduction start phase for initialacceleration of the motor (MT) 1 is determined in accordance with thepolarity information about the three-phase added induced voltages, whichis derived from the induced voltage determination section 51 of themotor drive control device according to the first embodiment, which isshown in FIGS. 1 and 5. Therefore, the energization of the determinedconduction start phase is initiated the next time the motor (MT) 1 issubjected to initial acceleration.

Further, as shown in FIG. 6, when the absolute value output ADCOUT,which corresponds to the three-phase added induced voltages(Vmu+)+(Vmu−), (Vmv+)+(Vmv−), (Vmw+)+(Vmw−), reaches the predeterminedreference value V_(TH), the conducting phase is changed to initiallyaccelerate the motor (MT) 1.

<Drive Voltage Generator for Initial Acceleration>

FIG. 7 is a diagram illustrating the configuration of the drive voltagegenerator 6C in the motor drive control device according to the firstembodiment, which is shown in FIG. 1.

The drive voltage generator 6C shown in FIG. 7 generates the drivevoltage VDRV, which determines the normal rotation torque for theaforementioned initial acceleration.

As shown in FIG. 7, the drive voltage generator 6C includes a digitalsubtractor 6C1, a digital phase compensator 6C2, a digital clamp circuit6C3, and a digital multiplier 6C4.

The digital subtractor 6C1 subtracts the current detection digitalsignal at the output ADCOUT of the A/D converter 4B from the currentinstruction value, which is supplied from the parameter setup register7A. Therefore, a digital error output signal corresponding to the errorbetween the current detection digital signal at the output ADCOUT of theA/D converter 4B and the current instruction value supplied from theparameter setup register 7A is supplied from the digital subtractor 6C1to the input terminal of the digital phase compensator 6C2.

When the digital phase compensator 6C2 performs a digital integrationprocess on the digital error output signal supplied from the digitalsubtractor 6C1, the output terminal of the digital phase compensator 6C2generates a digital PWM duty output signal PWM Duty, which specifies theduty of PWM drive for determining the normal rotation torque for theaforementioned initial acceleration.

The PWM duty upper-limit clamp signal CLPWM from the parameter setupregister 7A, which indicates a PWM duty upper-limit value, for instance,of 80%, a high-level clamp enable signal CLENA from the sequencer 53 inthe initial acceleration controller 5, and the digital PWM duty outputsignal PWM Duty from the digital phase compensator 6C2 are supplied tothe digital clamp circuit 6C3. Consequently, if the duty of PWM drivespecified by the digital PWM duty output signal PWM Duty is less than80% of the PWM duty upper-limit value, the output terminal of thedigital clamp circuit 6C3 generates a digital PWM duty output signal PWMDuty of less than 80%. If, on the other hand, the duty of PWM drivespecified by the digital PWM duty output signal PWM Duty is not smallerthan 80% of the PWM duty upper-limit value, the output terminal of thedigital clamp circuit 6C3 generates a value equivalent to 80% of the PWMduty upper-limit value specified by the PWM duty upper-limit clampsignal CLPWM. If a low-level clamp enable signal CLENA is supplied fromthe sequencer 53 in the initial acceleration controller 5 to the digitalclamp circuit 6C3, a digital PWM duty output signal PWM Duty having aduty within the range from 0% to 100% is directly generated from theoutput terminal of the digital clamp circuit 6C3 without being clamped.

The digital multiplier 6C4 generates a digital drive voltage VDRV bymultiplying the digital output signal of the digital clamp circuit 6C3by a PWM cycle count.

In response to the digital drive voltage VDRV generated from the digitalmultiplier 6C4 in the drive voltage generator 6C, the PWM modulator 6Bsupplies a PWM signal corresponding to the duty specified by the digitaldrive voltage VDRV to the input terminal of the output drive controller6A.

Consequently, if a high-level clamp enable signal CLENA is supplied tothe digital clamp circuit 6C3, the PWM signal generated from the PWMmodulator 6B is less than 80% of the PWM duty upper-limit value. If, onthe other hand, a low-level clamp enable signal CLENA is supplied to thedigital clamp circuit 6C3, the PWM signal generated from the PWMmodulator 6B is a duty within the range from 0% to 100%.

Duties of the PWM drive control signals UPWM, VPWM, WPWM generated fromthe output drive controller 6A are determined by the duty of the PWMsignal generated from the PWM modulator 6B. The initial accelerationoutput signals UPON, UNON, VPON, VNON, WPON, WNON of the initialacceleration controller 5 select a phase in which the output drivecontroller 6A outputs the PWM drive control signals.

Consequently, while a high-level clamp enable signal CLENA is suppliedto the digital clamp circuit 6C3, the duties of the PWM drive controlsignals UPWM, VPWM, WPWM correspond to a digital PWM duty output signalPWM Duty that is less than 80% of the PWM duty upper-limit value. On theother hand, while a low-level clamp enable signal CLENA is supplied tothe digital clamp circuit 6C3, the duties of the PWM drive controlsignals UPWM, VPWM, WPWM correspond to a digital PWM duty output signalPWM Duty having a duty within the range from 0% to 100%.

The motor drive current I_(SENSE) that has energized the power MOSFETsof the output driver 8 is converted to a voltage by the DC shuntresistor Rsns of the current detector 9A. The voltage is amplified bythe sense amplifier 9B. The current detection voltage CRNTOUT of thesense amplifier 9B is supplied to the A/D converter 4B in the A/Dconversion section 4. The current detection digital signal at the outputADCOUT of the A/D converter 4B is supplied to the digital subtractor 6C1in the drive voltage generator 6C.

<Initiation of Conduction for Initial Acceleration>

FIG. 8 is a diagram illustrating the configuration of the PWM modulator6B and of the output drive controller 6A that prevails at the beginningof conduction for initial acceleration in the motor drive control deviceaccording to the first embodiment, which is shown in FIG. 1.

As shown in FIG. 8, the PWM modulator 6B includes a subtractor 6B1, anadder 6B2, a PWM cycle counter 6B3, a divider 6B4, comparators 6B5, 6B6,and an AND circuit 6B7. The digital drive voltage VDRV generated fromthe drive voltage generator 6C is supplied to the subtractor 6B1 and tothe adder 6B2. The PWM cycle count is supplied to the subtractor 6B1 andto the PWM cycle counter 6B3. The PWM cycle counter 6B3 generates acount output CNT in response to the PWM cycle count. The result ofsubtraction performed by the subtractor 6B1 with respect to the digitaldrive voltage VDRV and PWM cycle count is converted by the divider 6B4to a PST signal, which is a digital value reduced to one-half of itsoriginal value. The PST signal is supplied to the adder 6B2 and to thecomparator 6B6. The adder 6B2 adds the PST signal to the digital drivevoltage VDRV. The result of this addition is supplied to the comparator6B5 as a PED signal. As the count output CNT from the PWM cycle counter6B3 is supplied to the comparators 6B5, 6B6, the comparators 6B5, 6B6digitally compare the count output CNT with the PED signal or with thePST signal. The results of digital comparisons performed by thecomparators 6B5, 6B6 are supplied to the two input terminals of the ANDcircuit 6B7. The output terminal of the AND circuit 6B7 generates a PWMsignal that serves as the output of the PWM modulator 6B.

As shown in FIG. 8, the output drive controller 6A includes AND circuits6A1, 6A3, 6A5 and NOR circuits 6A2, 6A4, 6A6. The initial accelerationoutput signals UPON, UNON, VPON, VNON, WPON, WNON generated from thedecoder 52 in the initial acceleration controller 5 are supplied to aplurality of input terminals of the AND circuits 6A1, 6A3, 6A5 and NORcircuits 6A2, 6A4, 6A6 in the output drive controller 6A. A plurality ofoutput terminals of the AND circuits 6A1, 6A3, 6A5 and NOR circuits 6A2,6A4, 6A6 in the output drive controller 6A generate the output controlsignals UPWM, UHIZ, VPWM, VHIZ, WPWM, WHIZ of the output drivecontroller 6A.

When the initial acceleration output signal UPON is at a high level(“1”), the PWM signal output from the PWM modulator 6B is selected bythe AND circuit 6A1 in the output drive controller 6A so that the outputcontrol signal UPWM is generated from the output terminal of the ANDcircuit 6A1 as a PWM selection output signal. Thus, in response to theoutput control signal UPWM, which serves as the PWM selection outputsignal of the output drive controller 6A, the U-phase pull-down powerMOSFET M4 in the output driver 8 shown in FIG. 1 is PWM-driven to the ONstate to energize the U-phase of the motor (MT) 1. When the initialacceleration output signals UPON, UNON are both at a low level (“0”),the AND circuit 6A1 does not generate the output control signal UPWM asthe PWM selection output signal, but the output terminal of the NORcircuit 6A2 generates the output control signal UHIZ. Thus, in responseto the output control signal UHIZ, which serves as a PWM non-selectionoutput signal of the output drive controller 6A, the U-phase pull-uppower MOSFET M1 and pull-down power MOSFET M4 in the output driver 8shown in FIG. 1 are maintained in the OFF state to leave the U-phase ofthe motor (MT) 1 unenergized.

When the initial acceleration output signal VPON is at the high level(“1”), the PWM signal output from the PWM modulator 6B is selected bythe AND circuit 6A3 in the output drive controller 6A so that the outputcontrol signal VPWM is generated from the output terminal of the ANDcircuit 6A3 as the PWM selection output signal. Thus, in response to theoutput control signal UPWM, which serves as the PWM selection outputsignal of the output drive controller 6A, the V-phase pull-down powerMOSFET M5 in the output driver 8 shown in FIG. 1 is PWM-driven to the ONstate to energize the V-phase of the motor (MT) 1. When the initialacceleration output signals VPON, VNON are both at the low level (“0”),the AND circuit 6A3 does not generate the output control signal VPWM asthe PWM selection output signal, but the output terminal of the NORcircuit 6A4 generates the output control signal VHIZ. Thus, in responseto the output control signal VHIZ, which serves as the PWM non-selectionoutput signal of the output drive controller 6A, the V-phase pull-uppower MOSFET M2 and pull-down power MOSFET M5 in the output driver 8shown in FIG. 1 are maintained in the OFF state to leave the V-phase ofthe motor (MT) 1 unenergized.

When the initial acceleration output signal WPON is at the high level(“1”), the PWM signal output from the PWM modulator 6B is selected bythe AND circuit 6A5 in the output drive controller 6A so that the outputcontrol signal WPWM is generated from the output terminal of the ANDcircuit 6A5 as the PWM selection output signal. Thus, in response to theoutput control signal WPWM, which serves as the PWM selection outputsignal of the output drive controller 6A, the W-phase pull-down powerMOSFET M6 in the output driver 8 shown in FIG. 1 is PWM-driven to the ONstate to energize the W-phase of the motor (MT) 1. When the initialacceleration output signals WPON, WNON are both at the low level (“0”),the AND circuit 6A5 does not generate the output control signal WPWM asthe PWM selection output signal, but the output terminal of the NORcircuit 6A6 generates the output control signal WHIZ. Thus, in responseto the output control signal WHIZ, which serves as the PWM non-selectionoutput signal of the output drive controller 6A, the W-phase pull-uppower MOSFET M3 and pull-down power MOSFET M6 in the output driver 8shown in FIG. 1 are maintained in the OFF state to leave the W-phase ofthe motor (MT) 1 unenergized.

As described above, the output drive controller 6A responds to theinitial acceleration output signals UPON, UNON, VPON, VNON, WPON, WNONgenerated from the decoder 52 in the initial acceleration controller 5and energizes the three-phase motor (MT) 1 for initial accelerationpurposes.

FIG. 9 is a waveform diagram illustrating how the PWM modulator 6B andthe output drive controller 6A operate at the beginning of conductionfor initial acceleration in the motor drive control device according tothe first embodiment, which is shown in FIG. 8.

FIG. 9 shows the PWM cycle count to be supplied to the subtractor 6B1and to the PWM cycle counter 6B3, the PED signal derived from theaddition performed in the adder 6B2, the count output CNT of the PWMcycle counter 6B3, the PST signal generated by the divider 6B4, and thePWM signal output from the PWM modulator 6B, which is generated from theoutput terminal of the AND circuit 6B7.

When the count output CNT is higher than the low-level PST signal andlower than the high-level PED signal as indicated at the leftmost pointin FIG. 9, the output of the comparator 6B6 is at the high level (“1”),and the output of the comparator 6B5 is at the high level (“1”). Thus,the PWM signal output from the PWM modulator 6B is at the high level(“1”).

When the count output CNT is higher than the low-level PST signal andhigher than the high-level PED signal as indicated at the secondleftmost point in FIG. 9, the output of the comparator 6B6 is at thehigh level (“1”), and the output of the comparator 6B5 is at the lowlevel (“0”). Thus, the PWM signal output from the PWM modulator 6B is atthe low level (“0”).

When the count output CNT is lower than the low-level PST signal andlower than the high-level PED signal as indicated at the third leftmostpoint in FIG. 9, the output of the comparator 6B6 is at the low level(“0”), and the output of the comparator 6B5 is at the high level (“1”).Thus, the PWM signal output from the PWM modulator 6B is at the lowlevel (“0”).

When the count output CNT is higher than the low-level PST signal andlower than the high-level PED signal as indicated at the fourth leftmostpoint in FIG. 9, the output of the comparator 6B6 is at the high level(“1”), and the output of the comparator 6B5 is at the high level (“1”).Thus, the PWM signal output from the PWM modulator 6B is at the highlevel (“1”).

When the count output CNT is higher than the low-level PST signal andhigher than the high-level PED signal as indicated at the fifth leftmostpoint in FIG. 9, the output of the comparator 6B6 is at the high level(“1”), and the output of the comparator 6B5 is at the low level (“0”).Thus, the PWM signal output from the PWM modulator 6B is at the lowlevel (“0”).

When the count output CNT is lower than the low-level PST signal andlower than the high-level PED signal as indicated at the sixth leftmostpoint in FIG. 9, the output of the comparator 6B6 is at the low level(“0”), and the output of the comparator 6B5 is at the high level (“1”).Thus, the PWM signal output from the PWM modulator 6B is at the lowlevel (“0”).

When the count output CNT is higher than the low-level PST signal andlower than the high-level PED signal as indicated at the rightmost pointin FIG. 9, the output of the comparator 6B6 is at the high level (“1”),and the output of the comparator 6B5 is at the high level (“1”). Thus,the PWM signal output from the PWM modulator 6B is at the high level(“1”).

Consequently, a period (duty) during which the PWM signal output fromthe PWM modulator 6B is at the high level (“1”) is determined by thedigital drive voltage VDRV generated from the drive voltage generator 6Cas indicated in FIG. 9. However, if the digital drive voltage VDRVgenerated from the drive voltage generator 6C is equal to the PWM cyclecount, the PST signal is zero so that the PED signal is the digitaldrive voltage VDRV, namely, the PWM cycle count. Therefore, the duty ofthe PWM signal output from the PWM modulator 6B is at risk of being100%.

As a result, in the above instance, the induced voltage to be developedin a non-conducting phase of the motor (MT) 1 will not be generated whenthe duty of the PWM signal is 100% as indicated in FIG. 14B. Therefore,the induced voltage determination section 51 cannot judge whether theinduced voltage is higher or lower than the predetermined referencevalue V_(TH). Hence, no change occurs in the output signal Dmode, whichindicates pull-up and pull-down conducting phases of the U-, V-, andW-phases of the motor (MT) 1 from the output of the induced voltagedetermination section 51. This makes it difficult to properly start upthe motor (MT) 1.

Under the above circumstances, the motor drive control device accordingto the first embodiment, which is shown in FIGS. 1 and 7, operates toinitiate the conduction for initial acceleration in such a manner thatthe sequencer 53 in the initial acceleration controller 5 supplies theclamp enable signal CLENA to the drive voltage generator 6C, and thatthe parameter setup register 7A supplies the PWM duty upper-limit clampsignal CLPWM to the drive voltage generator 6C.

The clamp enable signal CLENA can clamp an increase in the duties of PWMdrive control signals UPWM, VPWM, WPWM, which are generated from theoutput drive controller 6A when conduction starts for initialacceleration after the initial rotor position is identified by theinduced voltage detector 3. The PWM duty upper-limit clamp signal CLPWMsets the PWM duty upper-limit value for the duty clamp operation on thePWM drive control signals UPWM, VPWM, WPWM, which is enabled by theclamp enable signal CLENA.

It is therefore assumed that a high-level clamp enable signal CLENA issupplied from the sequencer 53 in the initial acceleration controller 5to the drive voltage generator 6C, and that a PWM duty upper-limit clampsignal CLPWM indicating a PWM duty upper-limit value, for instance, of80% is supplied from the parameter setup register 7A to the drivevoltage generator 6C. The error between the current detection digitalsignal at the output ADCOUT of the A/D converter 4B and the currentinstruction value supplied from the parameter setup register 7A iscalculated by the drive voltage generator 6C. A drive voltage VDRVcorresponding to the error is supplied from the output of the drivevoltage generator 6C to the input of the PWM modulator 6B. It should benoted, however, that the maximum drive voltage VDRV to be supplied islimited to 80% of the error.

As shown in FIG. 9, the drive voltage generator 6C generates the digitaldrive voltage VDRV whose maximum value is limited to 80% of the error.This ensures that the PWM modulator 6B supplies a PWM signal whose dutyis limited to 80% to the input of the output drive controller 6A. As aresult, the upper limit on an increase in the duties of the PWM drivecontrol signals UPWM, VPWM, WPWM generated from the output drivecontroller 6A can be clamped at 80% as specified by the PWM dutyupper-limit clamp signal CLPWM.

Consequently, referring to the waveform diagram of FIG. 9, the motordrive control device according to the first embodiment, which is shownin FIGS. 1 and 7, operates so that the duty of the PWM signal generatedfrom the PWM modulator 6B is clamped at a numerical value specified bythe PWM duty upper-limit clamp signal CLPWM, for example, at 80%. Hence,the induced voltage determination section 51 included in the motor drivecontrol device according to the first embodiment, which is shown inFIGS. 1 and 7, can judge whether the induced voltage is higher or lowerthan the predetermined reference value V_(TH). This makes it possible toproperly change the output signal Dmode, which is output from theinduced voltage determination section 51 to indicate the pull-up andpull-down conducting phases of the U-, V-, and W-phases of the motor(MT) 1. As a result, the motor (MT) 1 can be steadily started up.

<Operating Sequence>

FIG. 10 is an operating sequence diagram illustrating a rotor positionidentification operation based on a three-phase sense and a conductingoperation for initial acceleration, which are performed by the motordrive control device according to the first embodiment, which is shownin FIGS. 1 and 7.

As shown in FIG. 10, the rotor position identification operation basedon a three-phase sense starts in response to the high level of the startsignal Start for starting the rotation of the three-phase motor (MT) 1,which is supplied from the parameter setup register 7A, and to ahigh-level sense signal SENSE for instructing the induced voltagedetector 3 to detect induced voltages of three phases.

An enlarged diagram included in FIG. 10 shows the details of the rotorposition identification operation based on a three-phase sense.

At first, during a U-phase sense, offset calibration is performed afterthe U-, V-, and W-phases are all placed in an output high impedancestate Hi-Z. Subsequently, a short pulse current flows in the forwarddirection from the V-phase to the W-phase to measure the induced voltageVmu+ developed in a non-conducting U-phase. After the U-, V-, andW-phases are all placed in the output high impedance state Hi-Z again, ashort pulse current flows in the reverse direction from the W-phase tothe V-phase to measure the induced voltage Vmu− developed in thenon-conducting U-phase. In this manner, an added digital induced voltage(Vmu+)+(Vmu−) of the U-phase can be measured.

As for a V-phase sense and a W-phase sense, an added digital inducedvoltage (Vmv+)+(Vmv−) of the V-phase and an added digital inducedvoltage (Vmw+)+(Vmw−) of the W-phase can be measured in the same manneras for the above-described U-phase sense in accordance with the outputhigh impedance state Hi-Z, offset calibration, and induced voltage senseregarding the V-phase, and with the output high impedance state Hi-Z,offset calibration, and induced voltage sense regarding the W-phase.

As described with reference to the table at the bottom of FIG. 6, theinitial rotor position is identified in accordance with the polarityinformation (positive/negative) about the added digital induced voltagesof the U-, V-, and W-phases. Further, the normal rotation torque isgenerated to determine the conduction start phase for rotating the rotorin the normal direction.

During a first conducting operation for initial acceleration, the PWMdrive current flows to the two stator coils of the conduction startphase determined as described above for the purpose of performing afirst initial acceleration. Even while PWM drive is being provided forthe first conducting operation, the induced voltage developed in anon-conducting phase is detected. In other words, the absolute valueoutput ADCOUT of the absolute value circuit 514, which corresponds tothe three-phase added induced voltages (Vmu+)+(Vmu−), (Vmv+)+(Vmv−),(Vmw+)+(Vmw−), reaches the predetermined reference value V_(TH) asdescribed with reference to FIG. 6, the conducting phase is changed toinitially accelerate the motor (MT) 1. When the absolute value outputADCOUT for the first conducting operation reaches the predeterminedreference value V_(TH), a first conducting phase change is made toinitiate the PWM drive for a second conducting operation for initialacceleration. While the PWM drive is being provided for the secondconducting operation, the induced voltage developed in a non-conductingphase is also detected. The absolute value output ADCOUT for the secondconducting operation then reaches the predetermined reference valueV_(TH) so that a second conducting phase change is made to initiate thePWM drive for a third conducting operation for initial acceleration.

The motor drive control device according to the first embodiment, whichis shown in FIGS. 1, 5, and 7, operates in accordance with the operatingsequence for initial acceleration, which is shown in FIG. 10, so thatthe upper-limit duty values for PWM drive for the U-, V-, and W-phasescan be variably set as desired to a value not greater than 100%. Thisenables the induced voltage determination section 51 to determine thepolarities of the induced voltages in the U-, V-, and W-phases of themotor (MT) 1 and judge whether the induced voltages are higher or lowerthan the predetermined reference value V_(TH). Hence, the output signalDmode indicative of a conducting phase is properly generated so that themotor (MT) 1 can be properly started up.

More specifically, the parameter setup register 7A supplies the PWM dutyupper-limit clamp signal CLPWM to the drive voltage generator 6C, andthe sequencer 53 supplies a high-level clamp enable signal CLENA to thedrive voltage generator 6C. Therefore, when the PWM duty upper-limitclamp signal CLPWM for setting the PWM duty upper-limit value, forinstance, to 80% is supplied to the drive voltage generator 6C, theupper-limit duty values for PWM drive can be variably set as desired.

When the PWM drive for the third conducting operation depicted in theoperating sequence diagram of FIG. 10 is completed, the accelerationoperation changes from initial acceleration to final acceleration. Thischange can be made upon detection of the fact that the revolving speedof the motor (MT) 1 has reached a predetermined value. The change canalso be made upon detection of the fact that a predetermined period oftime has elapsed after a level change in the start signal START from lowto high or a level change in the sense signal SENSE from high to low.

During the final acceleration subsequent to the above accelerationoperation change, the induced voltage detector 3 in the motor drivecontrol device according to the first embodiment, which is shown in FIG.1, detects a combined voltage, which is a combination of the reversevoltage shown in FIG. 3 and the normalized induced voltage shown in FIG.4. Consequently, when the absolute value of the combined voltage reachesthe predetermined reference value V_(TH), the induced voltagedetermination section 51 in the initial acceleration controller 5 makesa conducting phase change for the purpose of subjecting the motor (MT) 1to the final acceleration. During the period of the final acceleration,the clamp enable signal CLENA supplied from the sequencer 53 to thedrive voltage generator 6C is at the low level. Therefore, in responseto the low-level clamp enable signal CLENA, the drive voltage generator6C directly generates, with clamping, a digital PWM duty output signalPWM Duty having a duty within the range from 0% to 100% at the outputterminal of the digital clamp circuit 6C3.

Even when the duty is 100%, the reverse voltage is detected during thefinal acceleration. Therefore, the acceleration operation can beperformed without causing a problem. Further, as the duty is not limitedanymore, the final acceleration of the motor (MT) 1 can be steadilyperformed by using a high acceleration torque.

Second Embodiment Improved Configuration of Motor Drive Control Device

When the motor drive control device according to the first embodiment,which is shown in FIGS. 1, 5, and 7, is used, the induced voltages inthe U-, V-, and W-phases of the motor (MT) 1 may fail to reach thepredetermined reference value V_(TH) during initial acceleration due,for instance, to a temperature rise caused by heat generation or to adecrease in the power supply voltage, thereby making it impossible tomake a conducting phase change, interrupting an ongoing initialacceleration, and causing the motor (MT) 1 to fail in startup.

A second embodiment of the present invention, which is a technologyeffective for reducing the possibility of startup failure in the motor(MT) 1, will now be described.

FIG. 11 is a diagram illustrating the configuration of the inducedvoltage determination section 51 in the initial acceleration controller5 of the motor drive control device according to the second embodiment.

The induced voltage determination section 51 according to the secondembodiment, which is shown in FIG. 11, differs from the induced voltagedetermination section 51 according to the first embodiment, which isshown in FIG. 5, in that a reference value change circuit 517 is addedto the former.

The second embodiment depicted in FIG. 11 is configured so that when theabsolute value output ADCOUT of the absolute value circuit 514 fails toreach the predetermined reference value V_(TH), a polarity determinationsignal POL of the absolute value circuit 514 changes to switch to aconducting phase advanced by one increment from a normal conductingphase. In such an instance, the reference value change circuit 517supplies a sub-reference value V_(THSUB), which is lower than thepredetermined reference value V_(TH), to an inverting input terminal− ofthe comparator 515. The change in the polarity determination signal POL,which occurs when the predetermined reference value V_(TH) cannot bereached, coincides with a change in the next conduction state. Thisensures that the next detection phase reverts to normal upon switchingto a conducting phase advanced by one increment. Further, switching hasbeen made to the sub-reference value V_(THSUB) lower than the referencevalue V_(TH), which was not detected once. Therefore, the secondembodiment depicted in FIG. 11 ensures that the absolute value outputADCOUT of the absolute value circuit 514 reaches the sub-reference valueV_(THSUB), which is relatively low.

Thus, a conducting phase change can be made. This makes it possible toavoid the interruption of the initial acceleration and reduce thepossibility of startup failure in the motor (MT) 1. In the inducedvoltage determination section 51 according to the second embodiment,which is shown in FIG. 11, the comparator output signal COM of thecomparator 515 and the polarity determination signal POL of the absolutevalue circuit 514 are both supplied to the conducting phase decoder 516.

FIG. 12 is a diagram that relates to the motor drive control deviceincluding the induced voltage determination section 51 according to thesecond embodiment, which is shown in FIG. 11, and illustrates thewaveforms of the reverse voltages of three-phase stator coils LU, LV, LWof the motor (MT) 1, the waveforms of the three-phase added inducedvoltages, the waveform of the absolute value output ADCOUT of theabsolute value circuit 514, the waveform of the comparator output signalCOM, and the waveform of the polarity determination signal POL.

As shown in FIG. 12, if the absolute value output ADCOUT from theabsolute value circuit 514 has reached the predetermined reference valueV_(TH), the comparator 515 generates a normal comparator output signalCOM. However, if, on the other hand, the absolute value output ADCOUTfrom the absolute value circuit 514 has not reached the predeterminedreference value V_(TH), the comparator 515 does not generate the normalcomparator output signal COM. More specifically, the comparator 515 doesnot generate a normal, high-level comparator output signal COM at atiming corresponding to an electrical angle of 60 degrees.

Consequently, the conducting phase decoder 516 in the induced voltagedetermination section 51 according to the second embodiment shown, forinstance in FIG. 11 makes time measurement to detect that the comparator515 does not supply the normal, high-level comparator output signal COMat a predetermined timing. Accordingly, the conducting phase decoder 516operates to switch to a conducting phase advanced by one increment froma normal conducting phase when the polarity determination signal POLchanges. Further, when a conducting phase change is made, the referencevalue change circuit 517 supplies the sub-reference value V_(THSUB),which is lower than the predetermined reference value V_(TH), to theinverting input terminal− of the comparator 515.

Hence, even if the absolute value output ADCOUT from the absolute valuecircuit 514 fails to reach the predetermined reference value V_(TH) dueto some abnormality as shown in FIG. 12, the polarity determinationsignal POL can make a conducting phase change. A change in the polaritydetermination signal POL coincides with a change in the next conductionstate. This ensures that the next detection phase reverts to normal uponswitching to a conducting phase advanced by one increment. Further,switching has been made to the sub-reference value V_(THSUB) lower thanthe reference value V_(TH), which was not detected once. Therefore, theabsolute value output ADCOUT of the absolute value circuit 514 reachesthe sub-reference value V_(THSUB), which is relatively low. Thus, asubsequent conducting phase change can be made. This makes it possibleto avoid the interruption of the initial acceleration and reduce thepossibility of startup failure in the motor (MT) 1.

As described above, if a temporary abnormality occurs during an initialacceleration operation, the second embodiment, which is depicted inFIGS. 11 and 12, can skip such an abnormally timed phase change andswitch to supply the sub-reference value, which is lower than thepredetermined reference value, to the inverting input terminal− of thecomparator 515. Therefore, at the next timing point, the absolute valueoutput ADCOUT of the absolute value circuit 514 reaches thesub-reference value V_(THSUB), which is relatively low. Hence, aconducting phase change can be made. This makes it possible to avoid theinterruption of the initial acceleration and reduce the possibility ofstartup failure in the motor (MT) 1. Upon detection of the fact that theabsolute value output ADCOUT of the absolute value circuit 514 hasreached the sub-reference value V^(THSUB), which is relatively low, apredetermined number of times, the reference value to be supplied to theinverting input terminal− of the comparator 515 can be changed from therelatively low sub-reference value V_(THSUB) to the predeterminedreference value V_(TH).

While the present invention contemplated by its inventors has beendescribed in detail in terms of preferred embodiments, it is to beunderstood that the present invention is not limited to those preferredembodiments, but extends to various modifications that nevertheless fallwithin the scope of the appended claims.

For example, the pull-up power MOSFETs M1, M2, M3 included in the outputdriver 8 are not limited to N-channel MOSFETs. P-channel MOSFETs mayalso be used as the pull-up power MOSFETs M1, M2, M3.

Further, the pull-up power MOSFETs M1, M2, M3 and pull-down powerMOSFETs M4, M5, M6 included in the output driver 8 are not limited toMOSFETs. Insulated-gate bipolar power transistors (IGBTs) may be used inplace of the power MOSFETs.

The foregoing embodiments have been described on the assumption thatthey are applied to a motor drive control device for providing drivecontrol of a three-phase DC motor. However, the present invention canalso be applied to a motor drive control device for providing drivecontrol of a multiphase DC motor.

Moreover, the present invention is applicable not only to a motor drivecontrol device that provides drive control of a spindle motor forrotating a magnetic disk of a hard disk drive (HDD), but also to a motordrive control device that provides drive control of a cooling fan motorfor a hard disk drive (HDD) or an optical disk drive.

What is claimed is:
 1. A motor drive control device comprising: avoltage detector; an A/D conversion section; an initial accelerationcontroller; output drive controllers; an output driver; and a currentdetector; wherein the output driver includes a plurality of powertransistors and an output pre-driver, the power transistors beingadapted to drive a multiphase DC motor, the output pre-driver beingadapted to drive a plurality of input electrodes of the powertransistors; wherein the current detector is capable of detecting amotor drive current that flows to the multiphase DC motor, detectedinformation about the motor drive current being converted to a currentdetection digital signal by the A/D conversion section; wherein theoutput drive controllers supply PWM drive output signals for PWM driveto the output pre-driver in such a manner as to minimize the errorbetween a current instruction signal and the current detection digitalsignal; wherein the voltage detector is capable of detecting an inducedvoltage developed across a stator coil of each phase of the multiphaseDC motor and generating a detected induced voltage; wherein, when themultiphase DC motor starts up, the initial acceleration controllerbecomes controlled and placed in an operating state, and in response tothe detected induced voltage generated from the voltage detector,supplies a plurality of initial acceleration output signals specifying aconducting phase for initial acceleration of the multiphase DC motor tothe output drive controllers; wherein the initial accelerationcontroller, the output drive controllers, and the output driver make aconducting phase change and perform the PWM drive to provide the initialacceleration of the multiphase DC motor in response to the detectedinduced voltage and to the error upon startup of the multiphase DCmotor, and wherein upper-limit duty values for the PWM drive outputsignals to be supplied from the output drive controllers to the outputpre-driver during the period of the initial acceleration can bearbitrarily set in the output drive controllers.
 2. The motor drivecontrol device according to claim 1, wherein the detected inducedvoltage generated from the voltage detector is converted to an inducedvoltage detection digital signal by the A/D conversion section, andwherein, before the initial acceleration, the initial accelerationcontroller can identify the position of a rotor of the multiphase DCmotor from a combination of pieces of polarity information carried bythe induced voltage detection digital signal concerning the phases ofthe multiphase DC motor.
 3. The motor drive control device according toclaim 2, wherein the initial acceleration controller determines a firstconducting phase for the initial acceleration in accordance with therotor position identified before the initial acceleration.
 4. The motordrive control device according to claim 3, wherein the initialacceleration controller makes the conducting phase change when theinduced voltage detection digital signal reaches a predeterminedreference value after the energization of the first conducting phase forthe initial acceleration.
 5. The motor drive control device according toclaim 4, wherein the motor drive control device further includes inputcircuits capable of receiving a control signal from the outside of themotor drive control device, and wherein a duty control signal, which isused to arbitrarily set the upper-limit duty values for the PWM driveoutput signals to be supplied from the output drive controllers to theoutput pre-driver during the period of the initial acceleration, can besupplied from the outside of the motor drive control device to theoutput drive controllers through the input circuits.
 6. The motor drivecontrol device according to claim 5, wherein the initial accelerationcontroller generates a clamp enable signal during the period of theinitial acceleration in response to a start signal for starting therotation of the multiphase DC motor, which is supplied from the inputcircuits, and wherein, during the period of the initial acceleration, inresponse to the clamp enable signal generated from the initialacceleration controller, the output drive controllers set theupper-limit duty values for the PWM drive output signals, which are tobe supplied to the output pre-driver, in accordance with the dutycontrol signal.
 7. The motor drive control device according to claim 6,wherein the initial acceleration controller detects that the inducedvoltage detection digital signal has not reached the predeterminedreference value at a predetermined timing, and then generates adetection signal, which indicates that the predetermined reference valueis not reached; wherein, in response to the detection signal, whichindicates that the predetermined reference value is not reached, theinitial acceleration controller generates a low-level sub-referencevalue that is lower than the predetermined reference value, and wherein,when the induced voltage detection digital signal reaches the low-levelsub-reference value, the initial acceleration controller makes theconducting phase change.
 8. The motor drive control device according toclaim 6, wherein the predetermined reference value can be supplied fromthe outside of the motor drive control device to the initialacceleration controller through the input circuits.
 9. The motor drivecontrol device according to claim 6, wherein the voltage detector, theA/D conversion section, the initial acceleration controller, the outputdrive controllers, and the output driver are integrated in asemiconductor chip having a semiconductor integrated circuit.
 10. Themotor drive control device according to claim 9, wherein the voltagedetector, the A/D conversion section, the initial accelerationcontroller, the output drive controllers, and the output driver, whichare integrated in the semiconductor chip having the semiconductorintegrated circuit, are capable of driving the multiphase DC motor,which is a three-phase DC motor serving as a spindle motor for rotatinga magnetic disk in a hard disk drive.
 11. A method of operating a motordrive control device that includes a voltage detector, an A/D conversionsection, an initial acceleration controller, output drive controllers,an output driver, and a current detector, wherein the output driverincludes a plurality of power transistors and an output pre-driver, thepower transistors driving a multiphase DC motor, the output pre-driverdriving a plurality of input electrodes of the power transistors;wherein the current detector is capable of detecting a motor drivecurrent that flows to the multiphase DC motor; wherein the currentdetector is capable of detecting a motor drive current that flows to themultiphase DC motor, detected information about the motor drive currentbeing converted to a current detection digital signal by the A/Dconversion section; wherein the output drive controllers supply PWMdrive output signals for PWM drive to the output pre-driver in such amanner as to minimize the error between a current instruction signal andthe current detection digital signal; wherein the voltage detector iscapable of detecting an induced voltage developed across a stator coilof each phase of the multiphase DC motor and generating a detectedinduced voltage; wherein, when the multiphase DC motor starts up, theinitial acceleration controller becomes controlled and placed in anoperating state, and in response to the detected induced voltagegenerated from the voltage detector, supplies a plurality of initialacceleration output signals specifying a conducting phase for initialacceleration of the multiphase DC motor to the output drive controllers;wherein the initial acceleration controller, the output drivecontrollers, and the output driver make a conducting phase change andperform the PWM drive to provide the initial acceleration of themultiphase DC motor in response to the detected induced voltage and tothe error upon startup of the multiphase DC motor, and whereinupper-limit duty values for the PWM drive output signals to be suppliedfrom the output drive controllers to the output pre-driver during theperiod of the initial acceleration can be arbitrarily set in the outputdrive controllers.
 12. The method according to claim 11, wherein thedetected induced voltage generated from the voltage detector isconverted to an induced voltage detection digital signal by the A/Dconversion section, and wherein, before the initial acceleration, theinitial acceleration controller can identify the position of a rotor ofthe multiphase DC motor from a combination of pieces of polarityinformation carried by the induced voltage detection digital signalconcerning the phases of the multiphase DC motor.
 13. The methodaccording to claim 12, wherein the initial acceleration controllerdetermines a first conducting phase for the initial acceleration inaccordance with the rotor position identified before the initialacceleration.
 14. The method according to claim 13, wherein the initialacceleration controller makes the conducting phase change when theinduced voltage detection digital signal reaches a predeterminedreference value after the energization of the first conducting phase forthe initial acceleration.
 15. The method according to claim 14, whereinthe motor drive control device further includes input circuits capableof receiving a control signal from the outside of the motor drivecontrol device; and wherein a duty control signal, which is used toarbitrarily set the upper-limit duty values for the PWM drive outputsignals to be supplied from the output drive controllers to the outputpre-driver during the period of the initial acceleration, can besupplied from the outside of the motor drive control device to theoutput drive controllers through the input circuits.
 16. The methodaccording to claim 15, wherein the initial acceleration controllergenerates a clamp enable signal during the period of the initialacceleration in response to a start signal for starting the rotation ofthe multiphase DC motor, which is supplied from the input circuits, andwherein, during the period of the initial acceleration, in response tothe clamp enable signal generated from the initial accelerationcontroller, the output drive controllers set the upper-limit duty valuesfor the PWM drive output signals, which are to be supplied to the outputpre-driver, in accordance with the duty control signal.
 17. The methodaccording to claim 16, wherein the initial acceleration controllerdetects that the induced voltage detection digital signal has notreached the predetermined reference value at a predetermined timing, andthen generates a detection signal, which indicates that thepredetermined reference value is not reached, wherein, in response tothe detection signal, which indicates that the predetermined referencevalue is not reached, the initial acceleration controller generates alow-level sub-reference value that is lower than the predeterminedreference value, and wherein, when the induced voltage detection digitalsignal reaches the low-level sub-reference value, the initialacceleration controller makes the conducting phase change.
 18. Themethod according to claim 16, wherein the predetermined reference valuecan be supplied from the outside of the motor drive control device tothe initial acceleration controller through the input circuits.
 19. Themethod according to claim 16, wherein the voltage detector, the A/Dconversion section, the initial acceleration controller, the outputdrive controllers, and the output driver are integrated in asemiconductor chip having a semiconductor integrated circuit.
 20. Themethod according to claim 16, wherein the voltage detector, the A/Dconversion section, the initial acceleration controller, the outputdrive controllers, and the output driver, which are integrated in thesemiconductor chip having the semiconductor integrated circuit, arecapable of driving the multiphase DC motor, which is a three-phase DCmotor serving as a spindle motor for rotating a magnetic disk in a harddisk drive.